TECHNICAL FIELD
[0001] The present invention is directed to an object detecting device with the use of a
pyroelectric infrared radiation sensor, and more particularly a surveillance device
for detecting the presence of a human in a room or space.
BACKGROUND ART
[0002] A typical object detecting device is disclosed in Japanese Utility Model Publication
No. 2-9891 and Japanese Patent Publication No. 6-3366. The device utilizes a pyroelectric
sensor generating a sensing current upon receiving an infrared radiation from a human
body, and an I/V converter that converts the sensing current into a voltage. The device
requires a voltage amplifier which amplifies the voltage from the I/V converter to
an amplified voltage of a level sufficiently enough to be compared with a threshold
for discriminating the presence of the human body. When the amplified voltage exceeds
the threshold, a detector provides a detection signal which is then processed to issue
a control output for activating an external device such as an alarming device and
the like. The device is designed such that, once the device is energized, all the
electronic components including voltage amplifier and the detector are made fully
operational as being supplied with a rated current from a power source. Accordingly,
the device will consume the power even in the absence of the infrared radiation of
a level not causing the detection signal, i.e., in the absence of the human body.
Thus, the prior device wastes the power and has to require frequent replacements of
a battery when it is used as the power source for the device.
DISCLOSURE OF THE INVENTION
[0003] In view of the above problem, the present invention has been achieved to provide
an improved object detecting device which is capable of reducing power consumption,
yet retaining reliable object detection. The object detecting device in accordance
with the present invention utilizes a pyroelectric sensor generating a sensing current
in accordance with changes in the amount of infrared radiation incident on the sensor
from an object. An I/V converter is provided to convert the sensing current into a
corresponding voltage which is then amplified by a voltage amplifier to an amplified
voltage. The device includes a detector with a level monitor which compares the amplified
voltage with a predetermined detection threshold so as to provide a detection signal
when the amplified voltage satisfies with a detection criterion with regard to the
detection threshold. The detection signal is then processed to issue a control output
for activating an external device. The voltage amplifier is capable of providing a
restricted voltage output of a low amplitude when receiving a limited source current
from the power source and providing a rated voltage output of a high amplitude when
receiving from the power source a rated source current higher than the limited source
current. The detector is added with a threshold selector which has, in addition to
the above detection threshold, a preliminary threshold lower than the detection threshold,
and is normally set to give the preliminary threshold to the level monitor. The level
monitor compares the restricted voltage output from the voltage amplifier with the
preliminary threshold and provides a wake-up signal when the restricted voltage output
satisfies a preliminary criterion with regard to the preliminary threshold. In response
to the wake-up signal, the threshold selector switches the preliminary threshold to
the detection threshold. Also included in the device is a mode selector which, in
response to the wake-up signal, provides an operation mode for supplying the rated
source current from a power source to the voltage amplifier such that the level monitor
compares the rated voltage output from the voltage amplifier with the detection threshold
for detection of the object, and otherwise provides a standby mode for supplying the
limited source current from the power source to the voltage amplifier. Thus, the device
can be kept in the standby mode of consuming less power while the pyroelectric sensor
generates a less current not critical to the detection of the object presence, and
can be switched to the operation mode where the voltage amplifier gives the rated
voltage output of a level sufficiently enough to make reliable detection once the
pyroelectric sensor generates a critical output. Accordingly, it is a primary object
of the present invention to provide an object detecting device which is capable of
reducing power consumption, yet assuring reliable detection.
[0004] The mode selector is designed to keep the operation mode continuously for a predetermined
time frame from the first advent of the detection signal and to switch it back to
the standby mode thereafter for avoiding unnecessary power consumption after the object
detection. In this connection, the mode selector is preferred to reset the time frame
to start each time the detection signal is followed by another detection signal within
the time frame, thereby extending the operation mode for successive and reliable detection
of the object.
[0005] The mode selector may be provided with a reset input for receiving a reset signal
from the external device. When the reset input is enabled, the mode selector operates
to switch the operation mode forcibly into a rest mode of keeping the limited source
current to be supplied to the voltage amplifier and at the same time disabling the
level monitor upon seeing the first advent of the detection signal, and keeps the
rest mode until receiving the reset signal at the reset input. Thus, the device can
be interlocked or closely associated with the external device so as to keep the power
consumption at a minimum level while the external device is reacting to make a dedicated
function such as turning on an illumination appliance in response to the control output,
thereby reducing the power consumption.
[0006] In order to start the device rapidly for reliable detection, the mode selector is
preferred to supply an initialization current greater than the rated source current
to the voltage amplifier only for a predetermined initialization time period immediately
upon energization of the device. Further, the mode selector is preferred to select
the rest mode for a predetermined stabilization time period immediately subsequent
to the initialization time period, and to switch the rest mode into the standby mode
thereafter. Thus, the voltage amplifier inherently requiring much initialization current
can be rapidly made ready for reliable operation. After the stabilization time period,
the components of the device can be made stable to be ready for reliable detection,
while eliminating a possibility of causing erroneous circuit operation leading to
a false detection due to unstable outputs of the voltage amplifier during the stabilization
time period.
[0007] The voltage amplifier may be of two-stage amplifier having a front-stage amplifying
section and a rear-stage amplifying section. In this connection, the mode selector
is configured to supply the limited source current to the front-stage and rear-stage
amplifying sections in the standby mode, and supply the limited source current to
the front-stage amplifying section and the rated source current to the rear-stage
amplifying section in the operation mode. With the use of the two-stage amplifier
and the associated scheme of only changing the level of the current being fed to the
rear-stage amplifying section, it is made possible to further reduce the power consumption
as compared to a case where the entire current to the amplifier is changed from the
limited level to the rated level.
[0008] Further, the voltage amplifier is preferred to generate the rated voltage output
which saturates at a level just above the detection threshold for the purpose of minimizing
the power consumption in the operation mode, yet retaining reliable detection.
[0009] Preferably, the threshold selector includes a first voltage divider providing the
preliminary threshold from a reference voltage and a second voltage divider providing
the detection threshold from the same reference voltage. The first voltage divider
is composed of a series combination of first resistors, while the second voltage divider
is composed of a series combination of second resistors. The first resistor is selected
to have a higher resistance than the second resistor in order to realize an advantageous
effect of reducing the power consumption made at the first voltage divider to give
the preliminary threshold with the use of the first resistors of high resistance,
while enabling the second voltage divider to give the detection threshold accurately
with the use of the second resistors of low resistance. Because of that first and
second resistors are preferably selected from those that can be integrated in a chip
for circuit miniaturization of the device, and also because of that the resistors
of the type available can give an accurate resistance value as the intended resistance
lowers, the second voltage divider makes the use of the second resistors of low resistance
to provide the accurate the detection threshold for reliable object detection therewith,
while the first voltage divider can consumes less power with the use of the first
resistors of high resistance in providing the preliminary threshold which is not critical
for object determination and could be rough as compared to the detection threshold.
For instance, the first resistor may be selected from a non impurity-doped polysilicon
resistor and a MOS (metal oxide semiconductor) transistor, while the second resistor
may be selected from an impurity-doped polysilicon resistor.
[0010] These and still other objects and advantageous features of the present invention
will become more apparent from the following description of a preferred embodiment
when taken in conjunction with the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011]
FIG 1 is a block diagram showing a circuit of an object detecting device in accordance
with a preferred embodiment of the present invention;
FIG. 2 is a circuit diagram showing a current regulator and its associated circuits
of the above device;
FIG. 3 is a circuit diagram of a voltage amplifier utilized in the above device;
FIG. 4 is a waveform chart illustrating the operation of the above device;
FIG. 5 is a waveform chart illustrating an operation of the mode selector;
FIG. 6 is a circuit diagram of a threshold selector utilized in the above device;
FIG. 7 is a circuit diagram showing a modified current regulator and its associated
circuit applicable to the above device; and
FIG. 8 is a circuit diagram of a voltage amplifier utilized in connection with the
above modified current regulator.
MODE FOR CARRYING OUT THE INVENTION
[0012] Referring now to FIG. 1, there is shown an object detecting device in accordance
with a preferred embodiment of the present invention. The device is utilized for surveillance
of a room or the like space and is adapted to be interlocked with an external device
such as an illumination appliance, an alarm and the like for activating the external
device upon detection of a human body in the room. The device utilizes a pyroelectric
sensor
10 which generates a sensing current in proportion to changes in the amount of incident
infrared radiation from the human body. The sensing current is fed to an I/V converter
20 where it is converted into a corresponding voltage. The voltage is then amplified
at a voltage amplifier
30 to provide a voltage output to a detector
40 for detection of the human body. The amplifier
30 has an offset voltage V
OFT around which the voltage output V
OUT varies, as shown in FIG. 4, in proportion to the amount of the sensing current from
the pyroelectric sensor
10.
[0013] The detector
40 includes a level monitor
50, a threshold selector
60 providing two thresholds, namely, a preliminary threshold TH
1 and a detection threshold TH
2 (>TH
1) to the level monitor
50, and a control output generator
70. The voltage output V
OUT from the amplifier
30 is compared at the level monitor
50 selectively with TH
1 (-TH
1) and TH
2 (-TH
2) to generate a wake-up signal when the voltage output satisfies a relation that V
OUT > TH
1 or V
OUT < -TH
1, and to generate a detection signal when the voltage output satisfies a relation
that V
OUT > TH
2 or V
OUT < -TH
2. The control output generator
70 is provided to issue, in response to the detection signal, a control output at an
output terminal
41 for activating the external device. As will be discussed later, the wake-up signal
is utilized to switch a standby mode, which is a default mode of consuming less power,
to an operation mode for reliable detection of the object. The standby mode is defined
to provide a limited source current to the I/V converter
20, the voltage amplifier
30, the level monitor
50, and the control output generator
70 for activating the same at a minimum performance level, while the operation mode
is defined to provide a rated source current higher than the limited current to the
same for activating the same at its full capability to obtain a reliable and consistent
detection result.
[0014] For this purpose, the device is provided with a mode selector
80 which includes a controller
90, a current regulator
100, and a timer
120. The controller
90 is provided to switch the standby mode to the operation mode and vice versa. The
current regulator
100 is configured to flow source currents of different levels designated by the controller
51. The source currents includes the limited source current of about 0.03 µA to 0.09
µA, for example, the rated source current of about 0.18 µA to 0.6 µA, for example,
and an initialization current higher than the rated current. As shown in FIG. 2, the
current regulator
100 includes a constant current supply
101, a plurality of FETs
102 to
107, and switches
111 to
113. The constant current supply
101 supplies a reference current I
101 from a power source Vdd through FET
102, while a series combination of FETs
103 and
104 is connected across the series combination of the current supply
101 and FET
102 to flow a mirror current I
103. Connected across FET
104 are three sets of series combinations each composed of each one of switches
111 to
113 and each one of FETs
105 to
107, as illustrated, such that the mirror current I
103 can vary by selective closing and opening of switches
111 to
113. As the mirror current I
103 varies, the I/V converter
20, the voltage amplifier
30, the level monitor
50, and control output generator
70 that are connected to receive a correspondingly varied voltage will be supplied with
one of the limited source current, the rated source current, and the initialization
source current. For instance, as illustrated in the figure, the voltage amplifier
30 includes two FETs
33 and
34 of which gates are connected to receive the voltage corresponding to the mirror current
I
103 in order to flow currents I
33 and I
34 as one of the limited source current, the rated source current, and the initialization
source current from the power source Vdd. Whereby, the voltage amplifier
30 can be selectively made to provide the restricted voltage output proportional to
the voltage from the I/V converter
20, to provide the rated voltage output proportional to the voltage from the I/V converter
20, and to complete the initialization, as will be discussed later.
[0015] As shown in FIG 3, the voltage amplifier
30 is of a two-stage amplifier including a front-stage amplifying section
31 and a rear-stage amplifying section
32. These sections
31 and
32 include current regulating FETs
33 and
34 which respond to the mirror current I
103 flowing through the current regulator
100 for flowing the source currents I
33 and I
34 from the power source Vdd to the front-stage amplifying section
31 and the rear-stage amplifying section
32, respectively. The gates of FETs
31 and
32 are commonly connected to receive the voltage corresponding to the mirror current
I
103 at a current control input
35. The front-stage amplifying section
31 includes a reference voltage input
36 for receiving a predetermined reference voltage and a voltage input
37 for receiving the voltage from the I/V converter
20 to amplify the same. The rear-stage amplifying section
32 includes an output terminal
38 for providing the amplified output to the level monitor
50.
[0016] Also, the I/V converter
20 is of two-stage configuration having two parallel current regulating FETs
23 and
24 which are connected between the power source Vdd and the ground and of which gates
are connected to receive the voltage corresponding to the current I
103 in order to flow currents I
23 and I
24 as one of the limited source current, the rated source current, and the initialization
source current, thereby providing the corresponding output to the voltage amplifier
30. Likewise, the level monitor
50 and the output controller
70 include current regulating FETs
53 and
73 respectively in order to flow individual currents I
53 and I
73 as one of the above different source currents. It is noted in this connection that
these source currents I
33, I
34, I
23, I
24, I
53 and I
73 may be made different from each other by selecting the corresponding FETs of different
characteristics.
[0017] The controller
90 is normally set to make the standby mode in which the current regulator
100 responds to flow the limited source currents, and the threshold selector
42 is normally set to give the preliminary threshold TH
1 to the level monitor
50 so that the level monitor
50 takes the voltage output V
OUT as the restricted voltage from the voltage amplifier
30, i.e., the voltage of low amplification and compares it with the preliminary threshold
TH1. When it is found that V
OUT > TH
1 or V
OUT < -TH
1, as shown in FIG. 4, the level monitor
50 provides the wake-up signal to the threshold selector
60 as well as to the controller
90 of the mode selector
80. Upon this occurrence, the threshold level selector
60 gives the detection threshold VTH
2 to the level monitor
50, and at the same time the controller
90 selects the operation mode to cause the amplifier
30 to provide the voltage output V
OUT as the rated voltage output, i.e., the voltage of high amplification. Thus, the level
monitor
50 is enabled to compare the voltage output V
OUT with the detection threshold TH
2 and issue the detection signal when V
OUT > TH
1 or V
OUT < -TH
1. The detection signal is indicative of the presence of the human body and is converted
into the control signal for activating the external device.
[0018] When the detection signal is issued, the controller
90 responds to activate the timer
120 to start counting time and switches the operation mode back to the standby mode after
the timer counting a predetermined time frame
T, thereby making the device to be ready for checking the next wake-up signal. In addition,
the controller
90 constantly checks whether or not subsequent detection signal is issued within the
time frame
T, and resets the timer
120 to start counting time each time the subsequent detection signal is acknowledged
within the time frame
T, thereby extending the time frame
T so long as the detection signal appears successively for notifying such event to
the external device.
[0019] The controller
90 is optionally provided with a reset terminal
91 for receiving a reset signal from the external device. When connecting the rest terminal
91 to the external device, the controller
90 is set to select a rest mode once the detection signal is acknowledged and keeps
the rest mode until receiving a reset signal from the external device. The rest mode
is defined to keep supplying the limited source current to the I/V converter
20, the amplifier
30, the level monitor
50, and the control output generator
70, and at the same time disabling the level monitor
50, i.e., neglecting the result of the level monitor
50. Thus, it is possible to minimize the power consumption while the external device
is responding, yet avoiding the occurrence of the wake-up signal which would provoke
the operation mode. This is particularly advantageous when the external device is
only required to activate for a limited time interval in response to the first advent
of the detection signal.
[0020] In order to reduce the power consumption at the amplifier
30 once the detection signal is issued, the amplifier
30 may be selected to saturate the voltage output V
OUT just above the detection threshold TH
2 or just below -TH
2 when supplied with the rated source current, as shown in FIG. 5.
[0021] As shown in FIG. 6, the threshold selector
60 includes a first voltage divider providing the preliminary threshold TH
1 and a second voltage divider providing the detection threshold TH
2 to the level monitor
50. The first voltage divider is a series combination of first resistors
61 connected in series with a switch
63 between the power source Vdd and the ground, while the second voltage divider is
a series combination of second resistors
62 connected in series with a switch
64 between the power source and the ground. The connection between the first resistors
61 is connected through a switch
65 to the level monitor
50, while the connection between the second resistors
62 is connected through a switch
66 to the level monitor. Normally, the switches
63 and
65 are closed to provide the preliminary threshold TH
1 to the level monitor
50. When receiving the wake-up signal from the level monitor
50, the switches
64 and
66 are closed to provide the detection threshold TH
2 to the level monitor
50. In view of that the preliminary threshold may be rough as it does not critical to
the detection of the human body, while the detection threshold have to be accurate
for reliable detection, and also that available resistors elements capable of being
integrated in a semiconductor chip together with other electronic components of the
device exhibit more accurate resistance value as the resistance value lowers, it is
contemplated in the present invention to use the first resistors
61 having the higher resistance and the second resistors
62 of lower resistance. Whereby, it is possible to give the reliable human detection
with the accurately determined detection threshold, yet reducing the power consumption
in providing the preliminary threshold with the use of the first resistors of high
resistance. For instance, the first resistor
61 is selected from a non impurity-doped polysilicon resistor or MOS (metal oxide semiconductor)
transistor, while the second resistor
62 is selected from impurity-doped polysilicon resistor.
[0022] Further, the device is designed to become stable rapidly upon being energized for
immediate and reliable object detection. For this purpose, the controller
90 responds to the throw-in of a power switch
130 of the device for providing an initialization time period during which the initialization
current higher than the rated current is allowed to flow in the I/V converter
20 and the voltage amplifier
30 for rapidly making these high current-consuming circuits operative, and the limited
current is allowed to flow to the level monitor
50 and the control output generator
60 of less current-consuming circuits. Immediately thereafter, the controller
90 selects the rest mode of disabling the output of the level monitor
50 for a predetermined stabilization time during which the limited source current is
supplied to make the whole circuits stable to be ready for reliable detection free
from any erroneous operation due to unstable outputs from the individual circuits,
particularly from the I/V converter
20 and the voltage amplifier
30. Thereafter, the controller
90 switches the rest mode to the standby mode, enabling the output of the level monitor
50 for making the intended operation of detecting the human body.
[0023] FIGS. 7 and 8 show a modified current regulator
100A and associated circuits which are similar to those utilized in the above embodiment
but are configured to switch the current being supplied to the rear-stage amplifier
of the I/V converter
20 and the rear-stage amplifier of the voltage amplifier
30, while constantly flowing the limited source current to the front-stage amplifiers
of the I/V converter
20, the front-stage amplifier of the voltage amplifier
30, the level monitor
50, and the control output generator
70. In this connection, the amplifier
30 is configured, as shown in FIG. 8, so that FET
33 of the front-stage amplifying section
31 and FET
34 of the rear-stage amplifying section
32 have individual gates to receive currents I
103A and I
103B of different levels or different voltage from the current regulator
100A, respectively through current control inputs
35A and
35B. As shown in FIG. 7, the current regulator
100A includes, in addition to a series combination of a constant current supply
101A and FET
102A connected across the power source Vdd, a front-end current generator
121 composed of FETs
103A, 104A and
105A and a switch
111A to provide a front-end mirror current I
103A, and a rear-end current generator
122 composed of FETs
103B, 104B and
105B, and switches
111B, 112B and
113B to provide a rear-end mirror current I
103B. The front-end mirror current I
103A is applied as a corresponding voltage to the gate of current regulating FET
23 of the front-stage amplifying section
21 of the I/V converter
20, the gate of current regulating FET
33 of the front-stage amplifying section
31 of the amplifier
30, the gate of current regulating FET
53 of the level monitor
50, and the gate of the current regulating FET
73 of the control output generator
70 in order to flow the limited source currents I
23, I
33, I
53, and I
73 from the power source Vdd to the individual circuits
20, 30, 50, and
70. Likewise, the rear-end mirror current I
103B is applied as a corresponding voltage to the gate of current regulating FET
24 of the rear-stage amplifying section
22 of the I/V converter
20, the gate of current regulating FET
34 of the rear-stage amplifying section
32 of the amplifier
30 in order to flow currents I
24 and I
34 from the power source Vdd to the rear-stage amplifying sections as one of the limited
source current, rated source current, and the initialization current by selective
activation of the switches
111B, 112B, and
113B.
[0024] In the absence of the wake-up signal from the level monitor
50, the controller
90 of the mode selector
80 sets the switches
111B, 112B, and
113B of the rear-end current generator
122 to make the rear-end mirror current I
103B nearly equal to the front-end mirror current I
103A, thereby flowing the limited source current I
24 and I
34, which are nearly equal to those currents I
23, I
33, I
53, I
73 caused by the front-end mirror current I
103A, to the rear-stage amplifying sections of the I/V converter
20 and the amplifier
30. When the wake-up signal is acknowledge, the controller
90 is switched to provide the rear-end mirror current I
103B larger than the front-end mirror current I
103A, thereby flowing the rated source current I
24 and I
34, which are greater than those currents I
23, I
33, I
53, I
73 caused by the front-end mirror current I
103A, to the rear-stage amplifying section of the I/V converter
20 and the amplifier
30. Thus, when the device is switched into the operation mode, the rated currents of
high level can be supplied only to the rear-stage amplifying sections of the I/V converter
20 and the amplifier
30 for the intended performance, thereby avoiding unnecessary high current consumption
otherwise made at the front-stage amplifying sections. The high initialization current
required at the very beginning of energizing the device can be fed only to the rear-stage
amplifying sections of the I/V converter
20 and the amplifier
30 while the limited source currents are fed to the front-stage amplifying sections
of the I/V converter
20 and the amplifier
30, as well as to the level monitor
50 and the control output generator
70. In this sense, the current regulator
100A is also configured to provide the initialization current higher than the rated source
current by selective activation of switches
111B to
113B.
[0025] The features disclosed in the foregoing description, in the claims and/or in the
accompanying drawings may, both separately and in any combination thereof, be material
for realising the invention in diverse forms thereof.
1. An object detecting device comprising:
a pyroelectric sensor (10) generating a sensing current in accordance with changes
in the amount of infrared radiation incident on said sensor from an object;
an I/V converter (20) which converts said sensing current from said pyroelectric sensor
into a corresponding voltage;
a voltage amplifier (30) which amplifies said voltage from the I/V converter into
an amplified voltage;
a detector (40) including a level monitor (50) which compares said amplified voltage
with a predetermined detection threshold (TH2) to provide a detection signal when said amplified voltage satisfies a detection
criterion with regard to said threshold, said detector responding to said detection
signal for issuing a control output which is indicative of the detection of the object
and is adapted to actuate an external device;
characterized in that
said voltage amplifier provides a restricted voltage output of low amplitude when
receiving a limited source current and provides a rated voltage output of high amplitude
when receiving a rated source current greater than said limited source current,
said detector includes a threshold selector (60) which has said detection threshold
(TH
2) and a preliminary threshold (TH
1) lower than said detection threshold, and which is normally set to provide the preliminary
threshold to said level monitor,
said level monitor compares said restricted voltage output from said voltage amplifier
with the preliminary threshold to provide a wake-up signal when the restricted voltage
output satisfies a preliminary criteria with regard to said preliminary threshold;
said threshold selector switches said preliminary threshold to said detection threshold
in response to said wake-up signal; and
said device further includes a mode selector (80) which, in response to the wake-up
signal, provides an operation mode for supplying said rated source current from a
power source to said voltage amplifier such that said level monitor compares the rated
voltage output with said detection threshold for detection of the object, and otherwise
provides a standby mode for supplying said limited source current to said voltage
amplifier from said power source.
2. The object detecting device as set forth in claim 1, wherein
said mode selector (80) keeps said operation mode continuously for a predetermined
time frame from the first advent of the detection signal and switches back forcibly
to the standby mode thereafter.
3. The object detecting device as set forth in claim 2, wherein
said mode selector (80) resets said time frame to start each time said detection
signal is followed by another detection signal within said time frame.
4. The object detecting device as set forth in claim 1, wherein
said mode selector has a reset input (91) for receiving a reset signal from said
external device, said mode selector switching said operation mode forcibly into a
rest mode for keeping said limited source current to supply to said voltage amplifier
from said power source and at the same time disabling said level monitor upon seeing
the first advent of said detection, and keeping said rest mode until receiving said
reset signal at said reset input.
5. The object detecting device as set forth in claim 1, wherein
said mode selector supplies an initializing current greater than said rated current
to said voltage amplifier only for a predetermined initialization time period immediately
upon energization of the device.
6. The object detecting device as set forth in claim 5, wherein
said mode selector selects a rest mode of supplying said limited source current
to said amplifier while disabling said level monitor for a predetermined stabilization
time period immediately subsequent to said initialization time period, and switches
the reset mode into said standby mode thereafter.
7. The object detecting device as set forth in claim 7, wherein
said voltage amplifier (30) is of two-stage amplifier having a front-stage amplifying
section (31) and a rear-stage amplifying section (32),
said mode selector supplying said limited source current to said front-stage and
rear-stage amplifying sections in said standby mode, and supplying said limited source
current to said front-stage amplifying section and supplying said rated source current
to said rear-stage amplifying section in said operation mode.
8. The object detecting device as set forth in claim 1, wherein
said voltage amplifier provides said rated voltage output which saturates at a
level just above said detection threshold.
9. The object detecting device as set forth in claim 1, wherein
said mode selector supplies the limited source current to said I/V converter (20)
in said standby mode, and supplies the rated source current to said I/V converter
in said operation mode.
10. The object detecting device as set forth in claim 1, wherein
said threshold selector (60) comprises a first voltage divider composed of a series
combination of first resistors (61) to provide said preliminary threshold (TH1) from a reference voltage, and a second voltage divider composed of a series combination
of second resistors (62) to provide said detection threshold (TH2) from said reference voltage source, said first resistors having higher resistance
than said second resistors.
11. The object detecting device as set forth in claim 10, wherein
said first resistor is selected from a non impurity-doped polysilicon resistor,
while said second resistor is selected from an impurity-doped polysilicon resistor.
12. The object detecting device as set forth in claim 10, wherein
said first resistors is selected from a MOS transistor, while said second resistor
is selected from an impurity doped polysilicon resistor.